(NECN/ABC) - Three additional arrests have been made in the murders of a couple in their Florida home, but police say as many as two more culprits may be at large as authorities try to get to the root of a heinous crime. Today, police say robbery was just one motive.

Late Monday night police made made an additional arrest in the murder of a Florida couple. Police say Gary Lamont Sumner is one of the individuals seen on surveillance tape approaching the home of Melanie and Byrd Billing the night they were killed. Cameras surrounding the home captured several men, some of whom police say remain at large, dressed in black and carrying long guns.

"We expect more arrests to be imminent in this case," says Escambia County Sheriff David Morgan. There are currently five men in custody in connection with this case. Authorities are focusing on one man in particular: 35-year old Leonard Gonzalez Jr., a certified black belt. He's seen on teaching children self-defense techniques in 2007, but police say Gonzalez also led a life of crime, possessing a lengthy criminal history.

For now, police will only say the motive appears to be robbery. The Billings, a wealthy couple, devoted their lives to raising more than a dozen children, several of whom had severe disabilities. At a benefit for children with down's syndrome in 2007, Byrd Billings celebrated the progress of one of his daughter's. "You know we have a child here who's 2-1/2 and just started walking. We think it's
ecstatic, you know," said Byrd Billings back in 2007.

Their home was built to accommodate the needs of their family. It features many rooms, and passageways. "It is a very big house. For them to be able to get to the parents room in less than 10 minutes without opening the children's rooms I find it so difficult to understand how they could have done that." says Nicole Lazore, author. Police say at least three of the couple's children may have come face to face with the suspected killers.